The Dawn spacecraft combines innovative state-of-the-art technologies pioneered by other recent missions with off-the-shelf components and, in some cases, spare parts and instrumentation left over from previous missions.

With its solar array in the retracted position (for launch), the Dawn spacecraft is 7 feet, 9 inches (2.36 meters) long -- about as long as a large motorcycle. With its wide solar arrays extended, Dawn is about as long as a tractor-trailer at 65 feet (19.7 meters).

During its nearly decade-long mission, the Dawn mission will study the giant asteroid Vesta and dwarf planet Ceres, celestial bodies believed to have accreted early in the history of the solar system. The mission will characterize the early solar system and the processes that dominated its formation.

Vesta and Ceres were chosen because, while both speak to conditions and processes early in the formation of the solar system, they developed into two different kinds of bodies.

Vesta is a dry, differentiated object with a surface that shows signs of resurfacing. It resembles the rocky bodies of the inner solar system, including Earth.

Ceres, by contrast, has a primitive surface containing water-bearing minerals, and may possess a weak atmosphere. It appears to have many similarities to the large icy moons of the outer solar system.

By studying both these two distinct bodies with the same complement of instruments on the same spacecraft, the Dawn mission hopes to compare the different evolutionary path each took as well as create a picture of the early solar system overall. Data returned from the Dawn spacecraft could provide opportunities for significant breakthroughs in our knowledge of how the solar system formed.

To carry out its scientific mission, the Dawn spacecraft will carry three science instruments whose data will be used in combination to characterize these bodies. These instruments consist of a visible camera, a visible and infrared mapping spectrometer, and a gamma ray and neutron spectrometer. In addition to these instruments, radiometric and optical navigation data will provide data relating to the gravity field and thus bulk properties and internal structure of the two bodies.

During its orbital studies, Dawn will investigate Vesta's and Ceres' internal structure, density and homogeneity by measuring their mass, shape, volume and spin state with radiometric tracking and imagery, and determine elemental and mineral composition. From this information scientists can determine the relationship between meteorites and their parent bodies, and the thermal histories of the bodies. From images of the surface, knowledge of their bombardment, tectonic and possibly volcanic history will be revealed.

The mission's scientific objectives are to:

Investigate the internal structure, density and homogeneity of two complementary protoplanets, Ceres and Vesta, one wet and one dry.

Determine surface morphology and cratering via near-global surface imagery in three colors at Vesta and in three at Ceres.

Perform radio tracking to determine mass, gravity field, principal axes, rotational axis and moments of inertia of both Vesta and Ceres.

Determine shape, size, composition and mass of both Vesta and Ceres.

Determine thermal history and size of each body's core.

Determine the spin axis of both Vesta and Ceres.

Understand the role of water in controlling asteroid evolution.

Test the prevailing scientific theory that Vesta is the parent body for a class of stony meteorites known as howardite, eucrite and diogenite, or "HED," meteorites; determine which, if any, meteorites come from Vesta.

Provide a geologic context for HED meteorites.

Obtain surface coverage with the mapping spectrometer from 0.25- to 5.0-micron wavelengths.

Obtain neutron and gamma ray spectra to produce maps of the surface elemental composition of each object, including the abundance of major rock-forming elements (oxygen, magnesium, aluminum, silicon, calcium, titanium and iron), trace elements (gadolinium and samarium), and long-lived radioactive elements (potassium, thorium and uranium).